A large number of documents describing the geometry of grooved tubes used in heat exchangers are known.
European Patent Application EP-A2-0 148 609 describes triangular or trapezoidal grooved tubes having the following characteristics:                an H/Di ratio between 0.02 and 0.03, where H designates the depth of the grooves (or height of the ribs), and Di the inside diameter of the grooved tube,        a helix angle β with reference to the tube axis between 7 and 30°,        an S/H ratio between 0.15 and 0.40, where S designates the cross-section of the groove, and        an apex angle α of the ribs between 30 and 60°0.        
These tube characteristics are suitable for phase change fluids, the tube performances being analyzed discretely when the fluid evaporates or condenses.
Japanese Patent Application No. 57-580088 describes tubes with V-shaped grooves, with H between 0.02 and 0.2 mm and an angle β between 4 and 15°. Similar tubes are described in Japanese Application No. 57-58094.
Japanese Patent Application No. 52-38663 describes tubes with V- or U-shaped grooves, with H between 0.02 and 0.2 mm, a pitch P between 0.1 and 0.5 mm, and an angle β between 4 and 15°.
U.S. Pat. No. 4,044,797 describes tubes with V- or U-shaped grooves similar to the aforementioned tubes.
Japanese Utility Model No. 55-180186 describes tubes with trapezoidal grooves and triangular ribs, with a height H of 0.15 to 0.25 mm, a pitch P of 0.56 mm, an apex angle a (referred to as angle θ in that document) typically equal to 73°, an angle β of 30°, and a mean thickness of 0.44 mm.
U.S. Pat. No. 4,545,428 and No. 4,480,684 describe tubes with V-shaped grooves and triangular ribs, with a height H between 0.1 and 0.6 mm, a pitch P between 0.2 and 0.6 mm, an apex angle α between 50 and 100°, and a helix angle β between 16 and 35°.
Japanese Patent No. 62-25959 describes tubes with trapezoidal grooves and ribs, with a groove depth H between 0.2 and 0.5 mm and a pitch P between 0.3 and 1.5 mm, the mean groove width being at least equal to the mean rib width. In one example, the pitch P is 0.70 and the helix angle β is 10°.
Finally, European Patent No. EP-B1-701 680, held by the applicant, describes grooved tubes, with flat-bottomed grooves and ribs of a different height H, a helix angle β between 5 and 50°, and an apex angle α between 30 and 60°, to ensure improved performance after the tubes are crimped and mounted in the exchangers.
In general, the technical and economic performance of the tubes, which results from the combination of tube specifications adopted (H, P, α, β, shape of grooves and ribs, etc.), generally arises from four considerations:                the characteristics relating to heat transfer (heat exchange coefficient), an area in which grooved tubes are greatly superior to non-grooved tubes, such that, for an equivalent heat exchange, the necessary length of a-grooved tube will be less than that of a non-grooved tube,        the characteristics relating to head loss, since minor head losses make it possible to use pumps or compressors of lower power, size and cost,        the industrial feasibility of the tubes and production speed, which determines the cost price of the tube for the tube manufacturer,        finally, the characteristics relating to the mechanical properties of the tubes, typically related to the type of alloys used or the mean tube thickness, which determines the weight of the tube per unit of length, and, therefore, influences its cost price.        
There are several problems with current designs.
Firstly, there are a great number and very wide variety of potential models with respect to grooved tubes, given that they generally aim to optimize heat exchange and decrease head loss.
Secondly, each of these models usually offers a wide range of possibilities, the parameters being generally defined by relatively broad ranges of values.
Finally, these models, when specified, relate to exchanges with two-phase fluids, i.e., those that use a fluid that evaporates in one part of the fluid circuit within the exchanger and condenses in another part of the circuit; no one grooved tube is used for both evaporation and condensation. Consequently, a person skilled in the art already has great difficulty determining the quintessential state of the art from such a large amount of data, which are sometimes contradictory.
A person skilled in the art knows that a typical commercially available tube, with triangular ribs as illustrated in FIG. 1, typically has the following characteristics: outside diameter De=12 mm, rib height H=0.25 mm, tube wall thickness Tf=0.35 mm, number of ribs N=65, helix angle β=18°, apex angle α=55°.